Thermoplastic materials include those materials that can be repeatedly melted and cooled to a solid. Thermoplastic material includes thermoplastic adhesives, sealants and waxes, referred to as “hot melt” materials. “Hot melt” materials are used in a wide variety of applications including the assembly of various types of products including furniture, doors, windows, automotive trim, etc., and the closing of boxes, containers, etc.
Typically, solid hot melt material, in various shapes and sizes, is supplied to a melter that includes a heated tank and/or a heated grid to produce molten hot melt material. Solid hot melt material can also be supplied in drums or barrels in which the material is melted by the use of a platen. After heating, the molten material can be pumped through a heated hose, to maintain the molten material at the required application temperature, to an applicator or dispenser, sometimes referred to as a “dispensing gun” or gun, dispensing handgun, or a gun module, comprising a valve and a nozzle.
Dispensing handguns can have various configurations that include top-feed and bottom-feed configurations that refer to the location on the handgun where a heated hose supplying hot melt material is connected to the handgun. Handguns of the foregoing type have been successfully used in many applications but their use can present manufacturing challenges in some instances. For example, it may be necessary to attach a relatively long nozzle to the end of the handgun barrel to apply the adhesive or sealant in “hard-to-reach” locations. Nozzles of this type can be about one to six inches in length for example. The handgun typically includes a heater, which can be a cartridge-type heater inside the barrel where the heated hose is coupled to the handgun. The heater maintains the hot melt material at the desired temperature and resultant viscosity.
The time between successive uses of the handgun can vary depending upon the particular production rate and can be affected by other factors such as lunch breaks, shift changes, etc. In some instances, the time between successive uses of the handgun can be long enough that there is a significant drop in temperature of the hot melt material in the nozzle as compared to the material in the handgun barrel. This can adversely affect the viscosity and flow characteristics of the hot melt material present in the nozzle such that it may not be useable. This problem is often resolved by depressing the handgun trigger for a sufficient period of time that a pump upstream of the heated hose, which is coupled to the handgun, forces the reduced temperature material out of the nozzle. While this procedure eliminates the unusable material in the nozzle, it results in additional material losses due to the nozzle purging and lost production line time, each of which adds to the cost of the production operation.
Also, handguns of the foregoing type, in particular bottom-feed handguns, may be subject to damage as a result of inadvertent misuse. Top-feed handguns may be hoisted upward after use and are less susceptible to damage. However, hoisting bottom-feed handguns overhead between applications is not practical due to the routing of the heated hose coupled to the handgun. If the handgun is placed on a workstation it may be pulled off due to the weight of the heated hose, which may result in damage to the handgun. Placing the handgun on the floor is also undesirable as a worker may inadvertently step on the handgun.